1. Field of the Invention
The invention relates to surface-modified non-halogenated mineral fillers, useful as flame retardants in olefin-based polymers.
2. Description of the Prior Art
Particulate mineral fillers, such as magnesium hydroxide and aluminum hydroxide, are widely used as non-halogenated flame retardants in a variety of hydrophobic polymers, particularly olefin-based polymers, e.g., polyethylene and polypropylene.
It is known that since these mineral fillers are hydrophilic in nature, there is a poor interaction between the mineral filler and the hydrophobic polymer. This poor interaction causes problems in the mechanical and physical properties of polymers incorporating these mineral fillers. Some of these physical problems are evidenced by reduced tensile stress and modulus, increased elongation (i.e., strain), and increased melt flow properties.
These problems are exacerbated by the fact that the mineral fillers are typically used in high amounts, i.e., exceeding fifty percent by weight of polymer. At such high amounts of incorporation, these mineral fillers dominate the chemical and mechanical properties of the polymer even further.
To mitigate these problems, particulate mineral fillers have often been surface-treated with surface modifiers to make them more compatible with the polymer base. Some of the surface modifiers that have been used include fatty acids, maleic anhydride-modified polymers, organosilanes, and silicones.
For example, Published PCT Application No. WO/9905688 to Eduardo et al., U.S. Pat. No. 6,576,160 to Eichler et al., U.S. Published Application No. 2004/0127602 to Schaeling et al., and U.S. Pat. No. 6,924,334 to Fukatani et al., disclose particulate magnesium hydroxide surface-treated with a variety of surface modifiers, including silanes.
However, there remains a need for particulate mineral fillers, and particularly magnesium hydroxide mineral fillers, which have been modified in such a way that they can be incorporated in polymers in flame-retarding amounts while imparting less or none of the above-described undesirable physical effects. There is also a need for increasing the weight percentages of mineral fillers in such polymers without the usual worsening of physical properties.
In addition, the mineral fillers currently used in the art, whether surface-modified or not, are typically highly hygroscopic, and accordingly, absorb significant amounts of water during storage and processing. The water absorbed in these mineral fillers cause further problems in the physical properties of polymers into which these water-adsorbed mineral fillers are incorporated. Therefore, there is also a particular need for mineral fillers more resistant to the absorption of water.